Forecasters are warning a tropical storm threatening to disrupt next week’s Republican convention in Florida could develop into a hurricane.

Tropical Storm Isaac took aim at the Dominican Republic and Haiti Thursday and it was expected to gain strength after drenching tiny islands in its whirl over the eastern entrance to the Caribbean. There was a chance it could dump rain on the convention.

No major damage was reported, but authorities in Puerto Rico said an elderly woman died in an accident while preparing for the storm.

U.S. forecasters said Isaac was likely to approach Hispaniola, the island shared by the Dominican Republic and Haiti, as a hurricane late Thursday or early Friday after intensifying over the warm waters of the Caribbean. It was predicted to move on to Cuba as a tropical storm, then perhaps head by Monday to Florida, where the Republicans will be gathering to nominate Mitt Romney for the presidency.

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In the eastern Caribbean, many seafront bars and restaurants remained open Wednesday night as lightning and thunder crackled and choppy surf slapped against piers and seawalls.

The storm was 360 kilometres south-southeast of Puerto Rico, early Thursday, with maximum sustained winds near 65 kph. Isaac was moving west near 21 kph, the U.S. National Hurricane Center said.

At the bar of the Fort Young Hotel in Dominica’s coastal capital of Roseau, a few tourists and locals drank cold beer and chatted over the sound of white-crested waves outside.

“The skies were very black and cloudy most of the day, but it’s been pretty quiet so far. Some rain, very little wind,” bartender Raymond Reynolds said Wednesday at the 71-room hotel on the jagged, densely forested island. “We’ve been through this before.”

In the foothills of Dominica’s Morne Aux Diables volcano, Tess Hunneybell, owner of Manico River Eco Resort, said most of Wednesday was “weirdly quiet” after she and others wrapped the resort’s signature treehouses in tarpaulin and nailed shut louvre doors.

As a precaution, Prime Minister Roosevelt Skerrit urged people to stay home from work. “I don’t want lives to lost,” he said.

As the storm approached, military authorities at the U.S. base in Guantanamo Bay, Cuba, cancelled several days of pretrial hearings in the case of five prisoners charged in the Sept. 11 terrorist attacks. They also planned to evacuate about 200 people, including legal teams and relatives of Sept. 11 victims.

In the U.S. Virgin Islands, along the harbour in St. Croix’s historic town of Christiansted, piers normally lined with pleasure boats were empty Wednesday. Business owners stacked sandbags around the doorways of pastel-colored buildings.

Schools and government offices in St. Croix were ordered to remain closed Thursday. St. Kitts had announced similar closures Wednesday.

With the storm expected to pass just south of Puerto Rico on Thursday, Gov. Luis Fortuno declared a state of emergency for the U.S. territory and activated the National Guard. He also cancelled classes and closed government agencies. Federal officials closed the popular San Felipe del Morro castle in Old San Juan.

Authorities in Puerto Rico reported that a 75-year-old woman died Wednesday in the northern city of Bayamon when she fell from a second-floor balcony while filling a barrel with water in preparation for the storm.

The U.S. Coast Guard closed all ports in Puerto Rico and the U.S. Virgin Islands to incoming commercial ships and warned that all commercial vessels bigger than 200 gross tons must leave or obtain permission to remain in port.

Downpours drenched the French island of Guadeloupe on Wednesday, said local chief meteorologist Norbert Aouizerats. Officials warned of swollen rivers and flooding in Martinique, where authorities urged people in low-lying areas to evacuate.

In the Dominican Republic, authorities banned boats from entering its waters and warned of heavy rains from Thursday through Saturday.

Liat airline and American Eagle cancelled flights to islands including Dominica, the U.S. Virgin Islands, Guadeloupe and Martinique.

On the island of Vieques, just east of Puerto Rico, people prepared for the government to temporarily shut off power.

Glenn Curry, an owner of Bananas Guesthouse, said he closed the restaurant and would move guests to a higher floor.

“I don’t think this is going to be a major storm, but it’s going to be noisy and unpleasant for a few hours,” he said.

In the meantime, another tropical depression was moving across the Atlantic. The depression had maximum sustained winds near 55 kph early Thursday and was expected to become a tropical storm later Thursday or on Friday. The depression was centred about 1,790 kilometres west of the Cape Verde Islands and moving west-northwest near 26 kph.